Multi-probe gauge for slab characterization

ABSTRACT

The present subject matter at-least provides an apparatus for characterization of a slab of a material. The apparatus comprises a plurality of frequency-domain optical-coherence tomography (FD-OCT) probes configured for irradiating the slab of material at at-least one location, and detecting radiation reflected from the slab of material or transmitted there-through. Further, a centralized actuation-mechanism is connected to the plurality of OCT probes for simultaneously actuating one or more elements in each of said OCT probes to at-least cause a synchronized detection of the radiation from the slab of material. A spectral-analysis module is provided for analyzing at least an interference pattern with respect to each of said OCT probes to thereby determine at least one of thickness and topography of the slab of the material.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No. 15/914,445, filed Mar. 7, 2018, now U.S. Pat. No. 10,209,058, and incorporated herein by reference in its entirety. This application is also related to U.S. patent application Ser. No. 15/410,328 filed on Jan. 19, 2017, and incorporated herein by reference in its entirety.

TECHNICAL FIELD

The embodiments discussed in this disclosure are related to a multi-probe gauge for slab characterization.

BACKGROUND

Frequency domain based optical coherence tomography (FD-OCT) probes have been used for characterization of properties of slabs of materials such as slab-thickness, slab structure and topography of the slabs. For ultra-thin slabs, industrially used measurement metrology is based on low-coherence interferometry. Such techniques are based upon an analysis of reflected infrared photon flux arriving from slab surfaces (layer-interfaces). The slab-thickness and characterization of the slab layer structure is obtained by analysis of an interferogram resulting from the FD-OCT probes.

A parameter that is often considered during metrology is a throughput measured in ‘number of slabs’ a tool can measure in a unit of time (usually expressed in slabs per hour). However, the throughput of the tool-measuring slabs is limited in the case of FD-OCT probes at-least due to limitations within the existing slab-handling and data-acquisition techniques. More specifically, data-acquisition speed is limited by the speed at which spectra can be acquired, which is in turn limited at least owing to independent operation of the plurality of probes positioned around the slab of material. In addition, conventional-mechanisms based on FD-OCT probes fail to take into account influence of vibration of the slab of material during the process of slab-characterization.

The subject matter claimed in this disclosure is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one example technology area where some embodiments described in this disclosure may be practiced.

SUMMARY

This summary is provided to introduce a selection of concepts in a simplified format that are further described in the detailed description of the present disclosure. This summary is neither intended to identify key or essential inventive concepts of the disclosure, nor is it intended for determining the scope of the invention or disclosure.

In one embodiment, the present subject matter provides an apparatus for characterization of a slab of material. The apparatus comprises a plurality of frequency-domain optical-coherence tomography (OCT) probes configured to irradiating the slab of material at at-least one location, and detecting radiation reflected from the slab of material or transmitted there-through. Further, a centralized actuation-mechanism is connected to the said plurality of OCT probes for actuating one or more elements in each of the OCT probes at a same time during irradiation of the slab of material to cause a synchronized-detection of the radiation from the slab of material by the plurality of OCT probes. A spectral-analysis module is configured to analyze an interference pattern of the radiation detected by each of the OCT probes to thereby determine at least one of thickness and topography of the slab of material.

In another embodiment, the present subject matter describes a method for characterization of a slab of material. The method comprises the positioning the slab of material on a chuck. The slab of material is irradiated at at-least one location by a plurality of frequency-domain optical-coherence tomography (OCT) probes. One or more elements within the plurality of OCT probes are actuated at a same time during the irradiation of the slab of material by the plurality of OCT probes to cause a synchronized detection of radiation reflected from the slab of material or transmitted there-through. Further, at least an interference pattern of the radiation detected by each of said OCT probe is spectrally analyzed for determining thickness with respect to one or more locations at the slab of material, and topography of the slab of material.

Overall, the present subject matter employs multiple synchronized FD-OCT probes to achieve an increased-throughput of a tool configured to characterize slab properties and reduce the influence of vibration over the results of measurement at-least due to a fast handling mechanism for the slab of material.

To further clarify advantages and features of the invention claimed herein, example descriptions and embodiments are rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only example embodiments of the invention and are therefore not to be considered limiting of its scope. The disclosure will be described and explained with additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates an example representation of system within a probe operating as a frequency domain optical coherence tomography (FD-OCT) probe;

FIG. 2 illustrates a second example representation of a system within the probe operating as the FD-OCT probe;

FIG. 3 illustrates a third example representation of a system within the probe operating as the FD-OCT probe;

FIG. 4 illustrates an example beam-assembly that may be implemented within the systems of FIG. 1-3;

FIG. 5 illustrates a fourth example representation of a system within the probe acting as the FD-OCT probe;

FIG. 6 illustrates a system comprising synchronized multiple FD-OCT probes for simultaneous measurement of properties of a slab of material;

FIG.7 illustrates a symmetric arrangement of two FD-OCT probes for measurement of the transparent and nontransparent slabs of materials for reduction of the noise caused by vertical mechanical vibration of a slab of material;

FIG.8 illustrates a type of asymmetric arrangement of two FD-OCT probes resulting from the relative motion of the slab of material with respect to probes due to vibration during the first portion of the vibration with respect to the slab of material;

FIG.9 illustrates another type of asymmetric arrangement of two FD-OCT probes with respect to the slab of material, resulting from motion of the slab of material due to vibration during the second portion of vibration cycle shown in FIG. 8;

FIG.10 illustrates occurrence of error during a slab-thickness measurement in case of the arrangement of the FD-OCT probes as depicted in FIG. 8 and FIG. 9 resulting from the vibratory-motion of the slab of material with respect to the FD-OCT probes;

FIG. 11 illustrates synchronized FD-OCT probes utilizing a spectrometer-detector combination for measurement of properties of a slab of material;

FIG. 12 illustrates operation of a spectrometer-detector combination as connected to the synchronized FD-OCT probes;

FIG. 13 illustrates synchronized FD-OCT probes utilizing a spectrometer-detector combination through an optical-switch for measurement of properties of the slab of material;

FIG. 14 illustrates a flowchart of an example method of measurement of properties of the slab of material through synchronized FD-OCT probes; and

FIG. 15 illustrates a computing device configured to facilitate measurement of properties of a slab of material through synchronized FD-OCT probes.

The elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the present disclosure is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the present disclosure as illustrated therein being contemplated as would normally occur to one skilled in the art to which the present disclosure relates.

The foregoing general description and the following detailed description are explanatory of the present disclosure and are not intended to be restrictive thereof

Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this present disclosure belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

Embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings.

FIG. 1 illustrates an example representation of a system 100 or arrangement within a probe operating as a frequency domain optical coherence tomography (FD-OCT) probe for measuring one or more properties of a slab of material 102. In some embodiments, the slab of material 102 may be any suitable piece of material that may have a relatively flat surface. For example, the slab of material 102 may be a silicon wafer, a semiconductor wafer, a glass plate or glass sheet (e.g., glass sheets used for wafer carriers, windows, flat panel displays, etc.), a polyester sheet (e.g., used for flexible panel displays), a polyimide sheet (e.g., used for flexible panel displays), sheet metal, a sandwich of various materials, such as those discussed above, or any other relatively flat element in which measuring properties of the element such as thickness or topography may be performed. A description and example of the system 100 can also be found at-least with respect to embodiments defined under FIG. 1 of the U.S. patent application Ser. No. 15/410328, filed Jan. 19, 2017, the complete-disclosure of which is incorporated herein by reference in its entirety.

The system 100 configured to inspect the slab of material 102 is arranged within the FD-OCT probe and accordingly denotes an internal assembly. In general, the system 100 may be configured to inspect the slab of material 102 in order to determine one or more properties of the slab of material 102 such as, for example, a thickness 106 of the slab of material 102 and a topography of a front surface 104 and/or a back surface 105 of the slab of material 102. To perform the inspection, the system 100 may include single mode optical fibers 108, 110, 112, and 114, a broadband light source 116, a beam forming assembly 118, a directional element 126, and an etalon filter 120 and a spectrometer 122 both controlled by a computer 124.

The broadband light source 116 may be configured to emit light over the optical fiber 108. The directional element 126 may be configured to receive the light from the broadband light source 116 over the optical fiber 108 and direct the light to the beam assembly 118 over the optical fiber 110. The beam assemblyl18 may be configured to receive the light over the optical fiber 110 and direct the light toward the slab of material 102, i.e. irradiate the slab of material 102. The beam assembly 118 may be further configured to receive the light reflected from the irradiated slab of material 102 and direct the light back to the directional element 126 over the optical fiber 110. The etalon filter 120, as controlled by the computer 124, may be configured to receive the light over the optical fiber 112 after the light has been reflected from the slab of material 102, filter the light, and direct the light over the optical fiber 114. The spectrometer 122, as controlled by the computer 124, may be configured to receive the light over the optical fiber 114, after the light has been filtered by the etalon filter 120 and after the light has been reflected from the slab of material 102, and spectrally analyze the light. More specifically, the spectrometer 122 may be coupled to one-dimensional array-detector (e.g. a charge coupled device) to capture electric-charge corresponding to an interference pattern (e.g., an interferogram) formed due to interference among the diffracted-frequencies due to dispersion of reference and reflected light within the spectrometer 122. The interferogram as obtained from the array-detector is used for spectral-analysis of the reflected-light from the slab of material 102. In some examples, the one dimensional array detector may be in-built within the spectrometer 122.

The spectral analysis of the light may include determining topography of the front surface 104 and/or the back surface 105 of the slab of material 102 and/or determining the thickness 106 of the slab of material 102. For such purposes, the computer 124 may be electrically coupled to the etalon filter 120 and to the spectrometer 122, and operates as a spectral-analysis module. The computer 124 may be configured to determine the thickness 106 of the slab of material 102 and/or determining a topography of the front-surface 104 the back surface 105 of the slab of material 102.

The computing-device 124 executes instructions to perform operations with respect to the spectrometer 122 in order to determine a topography of the front surface 104 and/or the back surface 105 of the slab of material 102 and/or determine the thickness 106 of the slab of material 102. In an example, the instructions to measure the thickness 106 of the slab of material 102 correspond to the following sequential-procedure as illustrated with respect to FIG. 1 in U.S. patent application Ser. No. 15/410328:

-   -   1. Measurement of the reference spectrum (as shown in FIG. 9A of         U.S. patent application Ser. No. 15/410328) of the broadband         light source 116     -   2. Measurement the signal spectrum (as shown in FIG. 9B of U.S.         patent application Ser. No. 15/410328) of the light reflected         from the slab of material 102 having a known refractive index n,         and passing through the etalon filter 120 having a known         thickness which is known to be slightly larger than the         thickness 106 of the measured slab of material 102.     -   3. Calculating a normalized spectrum (as shown in FIG. 9C of         U.S. patent application Ser. No. 15/410328) by dividing the         signal spectrum by the reference spectrum.     -   4. Calculating the frequency Ω of observed oscillations in the         normalized spectrum.     -   5. Calculating the thickness 106 of the slab of material 102         using Equation 34 of U.S. patent application Ser. No. 15/410328.

The topography of the front surface 104 of the slab of material 102 may be determined by placing the slab of material 102 on an XY motion stage perpendicular to light beam impinging front surface 104, wherein the front surface 104 is parallel to plane of motion of XY stage, and by collecting a data-set comprising the data set on a large number M comprising the x_(j) and y_(j) coordinates of the point where the beam is impinging the front surface 104 of the slab of material 102 and the distance between the a stationary lens (shown in FIG. 4 as 404) of the beam-forming assembly 118 and the front surface 104 of the slab of material 102 z_(j), where j=1 . . . M. The set of points (x_(j), y_(j), z_(j)) can then be used to construct a three dimensional map of the front surface 104 of the slab of material 102. A similar procedure may be performed to determine the topography of the back surface 105 of the slab of material 102.

FIG. 2 illustrates another example system 200 or arrangement within the one probe operating as the FD-OCT probe for inspecting a slab of material. A description and example of the system 200 may also be found at least with respect to embodiment defined under FIG. 2 of the aforesaid U.S. patent application Ser. No. 15/410328.

The system 200, in addition to components referred with the system 100, further includes a second directional element 213, an etalon filter 220, and a single mode optical fiber 215. The second directional element 213 may be configured to receive the light from the directional element 126 over the optical fiber 112 and direct the light to the etalon filter 220 over the optical fiber 215. The etalon filter 220 may be configured similarly to the etalon filter 120 of FIG. 1, except that the etalon filter 220 may be configured to receive the light from the second directional element 213 over the optical fiber 215 after the light has been reflected from the irradiated slab of material 102 and direct the light back to the second directional element 213 over the optical fiber 215. The spectrometer 122 of the system 200 may then be configured to receive the light from the second directional element 213 over the optical fiber 114.

FIG. 3 illustrates a third example representation of a system 300, within the probe operating as the FD-OCT probe, for inspecting the slab of material, arranged in accordance with at least some embodiments described in this disclosure. An example description of the system 300 may also be found at least with respect to embodiment defined under FIG. 3 of the aforesaid U.S. patent application Ser. No. 15/410328.

The system 300, in addition to elements in common with the system 100, may include a single mode optical fiber 317 and an etalon filter 320. The etalon filter 320 may be configured similarly to the etalon filter 120 of FIG. 1, except that the etalon filter 320 may be configured to receive the light over the broadband light source 116 over the optical fiber 317 before the light is directed toward the slab of material 102 and then, after filtering the light, direct the light over the optical fiber 108 to the directional element 126. Then, after the light has been reflected from the slab of material 102, the spectrometer 122 may be configured to receive the light from the directional element 126 over the optical fiber 112.

FIG. 4 illustrates an example beam assembly 400 containing a reference plane enabling absolute distance metrology, arranged in accordance with at least some embodiments described in this disclosure and implementable within the systems of FIG. 1-3 of the present subject matter. An example description of the assembly 400 can also be found at least with-respect to a beam-assembly 500, as defined under FIG. 5 within the aforesaid U.S. patent application Ser. No. 15/410328.

The beam assembly 400 may be employed as the beam assembly 118 in the systems 100, 200 and 300 of FIG. 1 till FIG. 3. The beam assembly 400 may include lenses 402 and 404. The beam assembly 400 may also optionally include a beam splitter 406 and a reflector 408. The lens 402 may be configured to receiving the light over the optical fiber 110 and collimate and direct the light toward the beam splitter 406. The beam splitter 406 may be configured to split the light from the lens 402 into first and second portions, direct the first portion of the light toward the lens 404, and direct the second portion of the light onto a reflector 408. The lens 404 may be configured to receive the first portion of the light from the beam splitter 406, direct the first portion of the light toward the slab of material 102, and direct the first portion of the light after being reflected from the slab of material back toward the beam splitter 406. Further, the reflector 408 may be configured to receive the second portion of the light from the beam splitter 406 and reflect the second portion of the light back toward the beam splitter 406. The beam splitter 406 may be further configured to combine the first portion of the light after being reflected from the slab of material 102 and the second portion of the light after being reflected from the reflector 408, and then direct the combined light toward the lens 402. Finally, the lens 402 may be configured to receive the combined light and direct the combined light over the optical fiber 110.

The beam assembly 400 may be employed to gauge the optical path difference (OPD) between the first portion of the light and the second portion of the light, which can be used to measure the distance between the front surface 104 of the slab of material 102 and the lens 404. As has been depicted with respect to the description in FIG. 1, distance between the front surface 104 of the slab of material 102 and the lens 404 assists in determination of topography of front and back surfaces of the slab of material 102.

FIG. 5 illustrates a fourth example system 500 within the FD-OCT probe for inspecting a slab of material, in accordance with at least some embodiments described in this disclosure. An example description of said system 500 can also be found at least with-respect to the system as defined under FIG. 4 of the aforesaid U.S. patent application Ser. No. 15/410328.

Although the beam splitter 406 and the reflector 408 may be beneficial in some embodiments of the beam assembly 400 as noted above with respect of FIG. 4 of the present subject matter, the present FIG. 5 omits the beam splitter 406 and the reflector 408. For example, in addition to elements in common with the system 100, the system 500 may include a first beam assembly 518 a and a second beam assembly 518. Since the light only passes through the beam assemblies 518 a and 518 b in a single direction in the system 500, the beam splitter 406 and the reflector 408 (otherwise present in FIG. 4 of the present subject matter) may be omitted.

More specifically, the beam assembly 518 a may be similar to the beam assembly 118 of FIG. 1 except that the beam-assembly 518 a is not configured to receive the light reflected back from the slab of material 102. Instead, the light directed from the beam assembly 518 a is transmitted through the slab of material 102 toward the second beam assembly 518 b. The second beam assembly 518 b may be configured to receive the light transmitted through the slab of material 102 and direct the light to the etalon filter 120 over the optical fiber 112. The etalon filter 120 may then be configured to receive the light from the second beam assembly 518 b over the optical fiber 112 after the light has been transmitted through the slab of material 102. Accordingly, the characterization of the slab of material 102 in the present FIG. 5 is based on light transmitted through the slab of material 102.

FIG. 6 illustrates a system 600 comprising multiple synchronized FD-OCT probes for simultaneous measurement of properties of a slab of material. More specifically, FIG. 6 describes multiple probes 602(1) . . . 602(n) for acquiring data synchronously for measurement of thickness and topography of the slabs of material. The assembly of each of said FD-OCT probe 602(1 to n) within the system 600 corresponds to the systems 100, 200, 300 and 500 as have been referred in the previous figures, wherein each of the probe 602 is an assembly of single mode optical fibers 108, 110, 112, 215, 317 and 114, the broadband light source 116, the beam forming assembly 118, the directional elements 126, 213, the etalon filter 120, 320 and the spectrometer 122. Further, all of the FD-OCT probes 602 in the system 600 measure a common slab of material 102 and connected to the common spectral-analysis module or the computing system 124. For sake of brevity, only two FD-OCT probes 602(1) and 602(n) have been shown as a part of the system 600.

Within the present system 600, the upper FD-OCT probe 602(1) is synchronized with lower FD-OCT probe 602(n) by means of a centralized actuation mechanism 2000 or a common electrical-cable 2000 whose one end is connected to all the FD-OCT probes. The other end of such electrical-cable 2000 is connected to a triggering source (e.g. a microcontroller) that sends pulses to actuate each of said FD-OCT probes at the same time such that the FD-OCT probes simultaneously detect the reflected radiation from the slab of material 102 and thereby enable a simultaneous measurement of distances from the slab of material 102 to each of the FD-OCT probes. In the present disclosure, reference to operations happening “simultaneously” or “at the same time” or being “synchronized” allows for margins of error in the simultaneous nature of, that may be less than 1%, 5%, or 10% depending on various implementation or materials constraints. Accordingly, upon having received a trigger through the electrical cable 2000, each of the probe out of the plurality of FD-OCT probes 602(1 to n) operates simultaneously. In other example, the actuation mechanism 2000 may be electro-mechanical, opto-electrical or opto-mechanical in nature. Largely, the simultaneous operation of the each of the probe 602 may be defined as a sequential-operation of:

-   -   a) irradiating the slab of material at a particular location;     -   b) detecting radiation reflected from the slab of material or         transmitted there-through;

Further, as may be understood with respect to FIG. 6, each of plurality of the probes 602(1 to n), inter alia, includes a combination of spectrometer 122 and uni-dimensional array detector 124. In other words, each of the probes 602 includes a respective spectrometer-array detector combination, wherein the spectrometer and array detector may either be integrated or separate from each other.

FIG. 7 illustrates a symmetric arrangement of two FD-OCT probes for measurement of the transparent and nontransparent slabs of materials for reduction of the noise caused by vertical mechanical vibration of a slab of material. More specifically, FIG. 7 illustrates the system 600 of FD-OCT probes for the purposes of reducing the influence of mechanical vibrations of the slab of material 102 during the course of determining thickness of the slab of material 102, which may be transparent, semi-transparent, or non-transparent in nature. As shown in FIG. 7, the system 600 comprises a pair of probes 602(1) and 602(2). ‘D’ represents a distance between the two probes 602(1) and 602(2) that may be pre-determined through any known means. Further, the distances H1 and H2, respectively depict the distance of the slab of material 102 from the first probe 602(1) and the second probe 602(2). Said distances are determined based on the spectral analysis performed with respect to each of the probe 602(1) and 602(2), as illustrated through the procedure illustrated in FIG. 1. Thereafter, the thickness ‘t’ of the slab of material 102 is determined based on following criteria (as illustrated in U.S. Pat. No. 7,116,429): t=D−H1−H2

The simultaneous calculation of H1 and H2 owing to a synchronized operation of the probe 602(1) and 602(2) coupled with a symmetric arrangement of probes 602(1) and 602(2) with respect to the slab of material 102 causes a precise determination of distances H1 and H2 and thereby a precise determination of the thickness ‘t’. Such measurement overcomes the influence of mechanical vibrations of the slab of material 102 during the course of determining thickness of the slab of material 102.

FIG. 8 illustrates a type of asymmetric arrangement of two FD-OCT probes resulting from the relative motion of the slab of material with respect to probes due to vibration during the first portion of the vibration with respect to the slab of material.

On the other hand, FIG. 9 illustrates another type of asymmetric arrangement of two FD-OCT probes with respect to the slab of material, resulting from motion of the slab of material due to vibration during the second portion of vibration cycle shown in FIG. 8.

Both FIG. 8 and FIG. 9 illustrate a non-synchronized arrangement of the probes 602(1) and 602(2), as a result of which both probes determine the distance from the slab of material 102 at different instants of time, say at t1 and t2, respectively. As illustrated in FIG. 8, at time ‘t1’, the distance between probe 602(1) and the slab of material 102 is observed to be H1A. As illustrated in FIG. 9, at time ‘t2’, the distance between probe 602(2) and the slab of material 102 is observed to be H2A. The asymmetric arrangement of two FD-OCT probes as depicted in FIG. 8 and FIG. 9 result from the relative motion of the slab of material with respect to probes due to vibration upwards and downwards, respectively. Such upward and downward vibration may also be referred as first and second portion of the vibration or vibratory-motion. Based on said readings, the thickness ‘tA’ gets determined as follows: tA=D−H1A−H2A

FIG.10 illustrates occurrence of error during a slab-thickness measurement in case of the arrangement of the FD-OCT probes as depicted in FIG. 8 and FIG. 9 resulting from the vibratory-motion of the slab of material with respect to the FD-OCT probes. Clearly, as indicated in FIG. 10, thickness ‘tA’ is substantially greater than the actual thickness ‘t’ of the slab of material 102 and gets determined as a substantially high thickness of the slab of material 102 owing to a continuous-vibration of the slab of material 102 with respect to the probes along y axis and non-synchronized operation of the probes 602(1) and 602(2). Accordingly, as may be understood, the synchronized operation of the probes 602(1) and 602(2) is able to determine the precise thickness ‘t’ despite the vibration of the slab of material 102 by virtue of measurement of the distances H1 and H2 as the same instant of time.

FIG. 11 illustrates synchronized FD-OCT probes utilizing a spectrometer-detector combination for measurement of properties of a slab of material. More particularly, the system 1100 depicted in FIG. 11 has synchronized FD-OCT probes 602 utilizing a centralized or sole spectrometer-detector combination for measurement of thickness and topography of slabs of material. More specifically, neither of the FD-OCT probes 602 in the system 1100 comprises an in-built spectrometer and detector combination. Instead, each of the probes 602 is rather aligned to a centralized spectrometer 1102 and detector 1104, thereby incurring significantly lower manufacturing costs when compared with the system 600. Further, the detector 1104 within the system is a 2 dimensional (2D) array detector, e.g., a charge coupled device having multiples rows of photo-sensitive elements.

FIG. 12 illustrates operation of a spectrometer-detector combination as connected to the synchronized FD-OCT probes. The spectrometer 1102 as illustrated in FIG. 12 is a dispersive-element based spectrometer. As shown in the figure, the light 1208, 1210 arriving from the slab of material 102 is directed to a same entrance slit 1202 of the dispersive spectrometer 1102 and accordingly positioned in separate locations along the entrance slit 1202, or in other words at different locations within an object-plane of spectrometer 1102. Upon having undergone diffraction from a dispersive element i.e. grating 1204 of the spectrometer 1102, a plurality of dispersed images of the slit 1202 are projected on the two-dimensional array detector 1104.

The light entering through the different points on the same slit 1202 form spectral lines across the detector 1104, such that each row (i.e. a uni-dimensional array) of light sensitive elements corresponds to a particular spectral line or spectrum out of the plurality of spectrums captured by the detector 1102. More specifically, each light originating from the slab of material 102 undergoes dispersion to produce a plurality of diffracted wavelengths that interfere with one another to produce a corresponding interferogram with respect to a particular light. Overall, a plurality of interferograms are captured as a plurality of spectral lines through the array detector 1102. The voltage signal corresponding to various spectral lines (i.e. each row of the array-detector) is multiplexed and thereafter digitized for serial-transmission through a cable to computer 124 (i.e. spectral analysis module) that further analyzes spectra in accordance with the ‘procedure’ as described within the description of FIG. 1. Accordingly, each spectral-line corresponding to each light received from probe 602(1 to n) is analyzed separately through spectral analysis module.

FIG. 13 illustrates synchronized FD-OCT probes utilizing a spectrometer-detector combination through an optical-switch for measurement of properties of the slab of material. A system 1300 as shown in FIG. 13 comprises synchronized FD-OCT probes utilizing the centralized spectrometer and detector combination (as depicted through FIG. 11) through an optical-switch 1302 for measurement of thickness and topography of the slab of material. More specifically, each of the plurality of probes 602(1 to n) are ported to the centralized spectrometer 1102 through an optical-switch 1304. In addition, said optical switch 1304 may be also appropriated to link a single broadband light source to the multiple probes 602(1 to n) for the purposes of irradiating the slab of material 102. In an example, the optical switch may correspond to either 1×N or N×1 configuration and may exemplarily be mechanical switch or Micro-electromechanical System (MEMS) switch.

FIG. 14 illustrates a flowchart of an example-method of measurement of properties (e.g. thickness and topography) of a slab of material through multiple FD-OCT probes 602(1 to n).

At step 1402, the slab of material 102 to be measured in placed within a chuck for initiating the measurement.

At step 1404, one or more elements within a plurality of FD-OCT probes 602(1 to n) are actuated at the same time by the centralized actuating mechanism 2000 to cause an operation thereof. Such operation of the plurality of probes 602 is achieved due to simultaneous actuation of each of the probe 602 by the actuation mechanism as described with respect to FIG. 6 to FIG. 11 and comprises:

-   -   a) irradiating the slab of material at-least one location by         said plurality of probes 602; and     -   b) synchronously detecting by the plurality of probes 602 the         radiation reflected from the slab of material or transmitted         there-through.

The synchronized-operation of the probes 602 in step 1404 further comprises filtering the detected radiation through an etalon-filter 120, 220, 320 present within each of the FD-OCT probe 602 to cause generation of the interference pattern with respect to each FD-OCT probe 602. An individual operation of each of the FD-OCT probe 602 corresponds to the method-steps as described with respect to the FIG. 10 of the aforesaid U.S. patent application Ser. No. 15/410328. Further, the radiation or light outputted from each of the FD-OCT probe 602 is dispersed by a dispersive element (e.g. grating) within the spectrometer 122, 1102 to thereby generate a plurality of spectrums. Each of the plurality of spectrums detected through the 2-dimensional array-detector 1104 thereafter undergo a spectral-analysis through the next step 1406. In order to facilitate such spectral-analysis, a plurality of signals (e.g. voltage) corresponding to the detected-spectrums and generated at the detector are multiplexed and thereafter digitized for transmission to the computer 124. The digitized-signal received at the computer 124 thereafter undergoes a digital to analog conversion through a digital-to-analog converter and de-multiplexing to recreate a plurality of analog signals at the computer 124 for the purposes of spectral-analysis.

At step 1406, the analog-signal(s) recreated at the computer 124 from the previous step 1404 are spectrally analyzed (in accordance with the procedure as described with respect to FIG. 1). Accordingly, the present step denotes a spectral-analysis of the interference pattern or spectrum corresponding to each of the probes. The spectral analysis in turn leads to a determination of properties of the slab of material such as a) thickness with respect to one or more locations at the slab of material; and b) topography of the slab of material.

FIG. 15 shows yet another example implementation in accordance with the embodiment of the present disclosure by depicting a computing device configured to facilitate measurement of properties of a slab of material through synchronized FD-OCT probes. More specifically, the present figure illustrates an example hardware configuration of the computer system 124 as a computing system 1500. The computer system 1500 can include a set of instructions that can be executed to cause the computer system 1500 to perform any one or more of the methods disclosed. The computer system 1500 may operate as a standalone device or may be connected, e.g., using a network, to other computer systems or peripheral devices.

In a networked deployment, the computer system 1500 may operate in the capacity of a server or as a client user computer in a server-client user network environment, or as a peer computer system in a peer-to-peer (or distributed) network environment. The computer system 1500 can also be implemented as or incorporated across various devices, such as a personal computer (PC), a tablet PC, a personal digital assistant (PDA), a mobile device, a palmtop computer, a laptop computer, a desktop computer, or any other machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. In an example implementation, the computer system 1500 may be a mobile computing cum display device capable of being used by a user. Further, while a single computer system 1500 is illustrated, the term “system” shall also be taken to include any collection of systems or sub-systems that individually or jointly execute a set, or multiple-sets, of instructions to perform one or more computer functions.

The computer system 1500 may include a processor 1502 e.g., a central processing unit (CPU), a graphics processing unit (GPU), or both. The processor 1502 may be a component in a variety of systems. For example, the processor 1502 may be part of a standard personal computer or a workstation. The processor 1502 may be one or more general processors, digital signal processors, application specific integrated circuits, field programmable gate arrays, servers, networks, digital circuits, analog circuits, combinations thereof, or other now known or later developed devices for analyzing and processing data The processor 1502 may implement a software program, such as code generated manually (i.e., programmed).

The computer system 1500 may include a memory 1504, such as a memory 1504 that can communicate via a bus 1508. The memory 1504 may include, but is not limited to computer readable storage media such as various types of volatile and non-volatile storage media, including but not limited to random access memory, read-only memory, programmable read-only memory, electrically programmable read-only memory, electrically erasable read-only memory, flash memory, magnetic tape or disk, optical media and the like. In one example, the memory 1504 includes a cache or random access memory for the processor 1502. In alternative examples, the memory 1504 is separate from the processor 1502, such as a cache memory of a processor, the system memory, or other memory. The memory 1504 may be an external storage device or database for storing data. The memory 1504 is operable to store instructions executable by the processor 1502. The functions, acts or tasks illustrated in the figures or described may be performed by the programmed processor 1502 executing the instructions stored in the memory 1504. The functions, acts or tasks are independent of the particular type of instructions set, storage media, processor or processing strategy and may be performed by software, hardware, integrated circuits, firm-ware, micro-code and the like, operating alone or in combination. Likewise, processing strategies may include multiprocessing, multitasking, parallel processing and the like.

As illustrated, the computer system 1500 may or may not further include a touch-sensitive display unit 1510, for outputting determined information as well as receiving a user's touch-gesture based inputs, such as drag and drop, single tap, multiple-taps, etc. The display 1510 may act as an interface for the user to see the functioning of the processor 1502, or specifically as an interface with the software stored in the memory 1504 or in the drive unit 1506.

Additionally, the computer system 1500 may include an input device 1512 configured to allow a user to interact with any of the components of system 1500. The computer system 1500 may also include a disk or optical drive unit 1506. The disk drive unit 1506 may include a computer-readable medium 1518 in which one or more sets of instructions 1514, e.g. software, can be embedded. Further, the instructions 1514 may embody one or more of the methods or logic as described. In a particular example, the instructions 1514 may reside completely, or at least partially, within the memory 1504 or within the processor 1502 during execution by the computer system 1500.

The present disclosure contemplates a computer-readable medium that includes instructions 1514 or receives and executes instructions 1514 responsive to a propagated signal so that a device connected to a network 1526 can communicate voice, video, audio, images or any other data over the network 1526. Further, the instructions 1514 may be transmitted or received over the network 1516 via a communication port or interface 1520 or using a bus 1508. The communication port or interface 1520 may be a part of the processor 1502 or may be a separate component. The communication port 1520 may be created in software or may be a physical connection in hardware. The communication port 1520 may be configured to connect with a network 1516, external media, the display 1510, or any other components in computing system 1500, or combinations thereof. The connection with the network 1516 may be established wirelessly as discussed later. Likewise, the additional connections with other components of the system 1500 may be established wirelessly. The network 1516 may alternatively be directly connected to the bus 1508.

The network 1516 may include wireless networks, Ethernet AVB networks, or combinations thereof. The wireless network may be a cellular telephone network, an 802.11, 802.16, 802.20, 802.1Q or WiMax network. Further, the network 1516 may be a public network, such as the Internet, a private network, such as an intranet, or combinations thereof, and may utilize a variety of networking protocols now available or later developed including, but not limited to TCP/IP based networking protocols. The system is not limited to operation with any particular standards and protocols. For example, standards for Internet and other packet switched network transmission (e.g., TCP/IP, UDP/IP, HTML, HTTP) may be used.

The present subject matter comprising multiple FD-OCT probes for characterization of one or more properties of a slab of material, at-least enables a substantially high data-acquisition speed through synchronized FD-OCT probes, i.e. through measuring the distances between the probes and slab at the same instant of time. This in turn successfully overcomes the influence of vibration of the slab of material during the process of slab-characterization, which may include the determination of one or more properties of the slab of material as discussed above. Moreover, the present subject matter provides a system low on manufacturing costs through employment of a centralized spectrometer-detector combination.

While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein.

The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein.

Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims. 

I claim:
 1. An apparatus for characterization of a slab of material comprising: a first frequency-domain optical-coherence tomography (OCT) probe configured to : irradiate the slab of material at a first location; and detect first radiation reflected from the slab of material at the first location in which the first radiation is reflected in response to irradiating the slab of material at the first location; a second frequency-domain OCT probe configured to : irradiate the slab of material at a second location; and detect second radiation reflected from the slab of material at the second location in which the second radiation is reflected in response to irradiating the slab of material at the second location; a centralized actuation mechanism communicatively coupled to the first OCT probe and the second OCT probe and configured to actuate the first OCT probe and the second OCT probe at a same time during irradiation of the slab of material at the first location and at the second location to cause a synchronized detection of the first radiation by the first OCT probe and of the second radiation by the second OCT probe; and a spectral-analysis module configured to analyze the first radiation reflected from the slab of material and the second radiation reflected from the slab of material to thereby determine at least one of thickness and topography of the slab of material.
 2. The apparatus as claimed in claim 1, wherein the first OCT probe comprises a beam forming assembly configured to: receive the first radiation over an optical fiber from a radiation-source and direct the first radiation toward the slab of material; and detect the first radiation reflected from the slab of material.
 3. The apparatus as claimed in claim 2, wherein the first OCT probe comprises an etalon-filter in optical communication with the beam-forming assembly, the etalon-filter is configured to: receive the first radiation over the optical fiber either before the first radiation is directed toward the slab of material or after the radiation has been reflected from the slab of material, filter the received first radiation to cause generation of a first interference pattern, wherein the analyzing of the first radiation reflected from the slab of material includes analyzing the first interference pattern.
 4. The apparatus as claimed in claim 1, wherein the first OCT probe further comprises: a spectrometer in optical-communication with the etalon-filter and configured to disperse the first radiation reflected from the slab of material to generate a first spectrum; and a unidirectional array detector configured to detect the first spectrum and trigger a spectral-analysis thereof by the spectral-analysis module such that the spectral analysis of the first spectrum is included in the analysis of the first radiation reflected from the slab of material.
 5. The apparatus as claimed in claim 1, further comprising a centralized spectrometer in optical-communication with the first OCT probe and configured to: disperse the first radiation output from the first OCT probe during irradiation of slab of material by the first OCT probe to generate a first spectrum; and disperse the second radiation output from the second OCT probe during irradiation of slab of material by the second OCT probe to generate a second spectrum; and a two-dimensional array detector configured to detect the first spectrum and the second spectrum and trigger a spectral-analysis thereof such that the spectral analysis of the first spectrum is included in the analysis of the first radiation reflected from the slab of material and such that the spectral analysis of the second spectrum is included in the analysis of the second radiation reflected from the slab of material.
 6. The apparatus as claimed in claim 5, wherein the two-dimensional array detector includes: a first group of radiation-detecting elements corresponding to the first OCT probe and configured to detect the first spectrum; and a second group of radiation-detecting elements corresponding to the second OCT probe and configured to detect the second spectrum.
 7. The apparatus described in claim 5, further comprising: a multiplexer connected to the array detector and configured to multiplex a first signal corresponding to the first spectrum with a second signal corresponding to the second spectrum; and an analog to digital-converter configured to digitize the received multiplexed signal for transmission to the spectral-analysis module.
 8. The apparatus as claimed in claim 1, wherein the first location corresponds to a first side of the slab of material and the second location corresponds to a second side of the slab of material.
 9. The apparatus as claimed in claim 1, wherein the first location and the second location are along a same line that runs perpendicular to and through the first side and the second side.
 10. The apparatus as claimed in claim 1, wherein the first location and the second location are on a same side of the slab of material.
 11. A method for characterization of a slab of material comprising: positioning the slab of material on a chuck; actuating a first frequency-domain optical-coherence tomography (OCT) probe such that the first OCT probe irradiates the slab of material at a first location and detects first radiation reflected from the slab of material at the first location in which the first radiation is reflected in response to irradiating the slab of material at the first location; actuating a second frequency-domain OCT probe simultaneously with the actuating of the first OCT probe such that the second OCT probe irradiates the slab of material at a second location and detects second radiation reflected from the slab of material at the second location in which the second radiation is reflected in response to irradiating the slab of material at the second location and second radiation is detected synchronously with the detection of the first radiation by the first OCT probe; and spectrally analyzing the detected first radiation and the detected second radiation to determine at least one of: thickness with respect to one or more locations at the slab of material; and topography of the slab of material.
 12. The method as claimed in claim 11, further comprising filtering the detected first radiation through an etalon-filter within the first OCT probe to cause generation of a first interference pattern of the detected first radiation, wherein spectrally analyzing the detected first radiation includes spectrally analyzing the first interference pattern.
 13. The method as claimed in claim 12, further comprising: dispersing the first radiation output from the first OCT probe during irradiation of slab of material by the first OCT probe to generate a first spectrum; and dispersing the second radiation output from the second OCT probe during irradiation of slab of material by the second OCT probe to generate a second spectrum; and detecting, by a two-dimensional array detector, the first spectrum and the second spectrum to trigger a spectral-analysis thereof such that the spectral analysis of the first spectrum is included in the analysis of the first radiation reflected from the slab of material and such that the spectral analysis of the second spectrum is included in the analysis of the second radiation reflected from the slab of material.
 14. The method as claimed in claim 13, wherein the two-dimensional array detector includes: a first group of radiation-detecting elements corresponding to the first OCT probe and configured to detect the first spectrum; and a second group of radiation-detecting elements corresponding to the second OCT probe and configured to detect the second spectrum.
 15. The method as claimed in claim 13, further comprising: multiplexing a first signal corresponding to the first spectrum with a second signal corresponding to the second spectrum; and digitizing the received multiplexed signal for spectral analysis.
 16. The method as claimed in claim 11, wherein the simultaneous actuation of the first OCT probe and the second OCT probe includes simultaneously measuring a first distance between the slab of material and the first OCT probe and a second distance between the slab of material and the second OCT probe.
 17. The method as claimed in claim 11, wherein the first location corresponds to a first side of the slab of material and the second location corresponds to a second side of the slab of material.
 18. The method as claimed in claim 11, wherein the first location and the second location are along a same line that runs perpendicular to and through the first side and the second side.
 19. The method as claimed in claim 11, wherein the first location and the second location are on a same side of the slab of material. 